Round die rolling is a processing involving: pressing a die as a rolling tool against a material to be processed while rotating the die; and rotating the material to be processed to mold the material. In the processing, an extremely stringent processing such as thread rolling or gear rolling is performed.
Therefore, a lubricating oil to be used in the round die rolling is requested to express such high processing performance as described below under stringent lubricating conditions: tool wear is reduced, and the surface roughness of a processed product is alleviated.
By the way, in the field of a lubricating oil for metal working, a chlorine-based compound such as a chlorinated paraffin or a chlorinated fatty acid ester has been widely used as an effective additive for improving processing performance under stringent conditions. In recent years, however, it has been pointed out that the chlorine-based compound involves such problems as described below in terms of safety to a human body and environmental pollution: the compound has carcinogenicity, and dioxin is produced at the time of the incineration of a waste liquid containing the compound. In view of the foregoing, the use of the chlorine-based compound has been avoided. As a result, the so-called non-chlorine-based lubricating oil blended with no chlorine-based compound has started to be demanded.
Therefore, a lubricating oil to be used in the round die rolling has been requested to show high processing performance without using any chlorine-based compound.
In addition, a bearing for a round die constituted of a nonferrous alloy such as bronze must continue to support a load generated by a processing, so a lubricating oil to be used in the round die rolling is typically adapted to lubricate the bearing as well.
Therefore, a lubricating oil for round die rolling is requested to have the following performance as well as the processing performance: lubricity in the bearing is improved, and the life of the bearing is lengthened.
A cutting oil, a lubricating oil for ordinary rolling, or the like has been conventionally diverted for such a lubricating oil for round die rolling. For example, Patent Documents 1 and 2 each relate to the invention of a cutting oil, and each describe that the cutting oil can be diverted for rolling (see, for example, the paragraph [0157] of Patent Document 1 and the paragraph [0002] of Patent Document 2).
At present, however, the use of a lubricating oil except a lubricating oil for round die rolling such as the cutting oil precludes continuous performance of normal round die rolling because the lubricating oil cannot be provided with the following performance together with the above-mentioned processing performance: lubricity in a bearing is improved, and the life of the bearing is lengthened.
Therefore, a lubricating oil composition for round die rolling which shows excellent processing performance without using any chlorine-based compound, and can improve lubricity in a bearing to lengthen the life of the bearing is expected to appear.
Patent Document 1: JP 2005-272818 A
Patent Document 2: JP 2005-187650 A